Edward Glaeser Commentary: California's Green Meanies

California environmentalists are tireless in their efforts to stop new development. But for the good of the planet, maybe they should lighten up. Indeed, the best thing that environmentalists can do to fight global warming is to encourage new construction in the state, especially in the areas with the most temperate climates.

California's metropolitan areas are, by far, the greenest in the country. Matthew Kahn, an environmental economist at UCLA, and I have estimated the carbon emissions associated with a new household in different parts of the country. Our estimates hold constant family size and income, and include driving emissions, public transport, home heating and electricity. We've found that the four greenest metropolitan areas in the United States are San Francisco, San Jose, San Diego and Los Angeles.

Why is California so green? The use of clean energy and efficient appliances deserves some credit, but the biggest factor is climate.

The state's weather is just better than that of the rest of the United States. As I write these words, my New England home is emitting an awful lot of carbon just to get itself to 60 degrees. An average Boston home emits more than twice as much carbon, because of home heating, as a home in San Jose.

Humid Houston leads the country in days when the temperature rises above 90 degrees, but since the last census, that area's population has increased by more than 900,000, which is greater than the growth of Los Angeles, San Diego, San Francisco and San Jose put together. Our estimate is that a typical Houston household uses almost four times more electricity than a comparable household in San Francisco.

Much of America struggles with cold winters and hot summers. Making such difficult climates comfortable for humans requires a lot of energy. By contrast, much of coastal California is pretty pleasant year-round, requiring far less energy. The natural implication is that to reduce carbon emissions, more Americans should live in temperate California.

But just as global warming has strengthened the case for California's expansion, the state's rate of growth is faltering. After sustaining a double-digit growth rate for much of the mid-20th century, California's population grew just 7.9% from 2000 through 2007, only slightly more than the growth rate of the country as a whole.

The reduction in California's growth rate does not reflect economic decline -- the state still has enormous wealth. It does not reflect a lack of demand for California's amenities. Even after the housing bust, the state's home prices remain among the highest in the world. And although California is a populous state, it still has plenty of land. Santa Clara County, the home of Silicon Valley, only has about 2.2 people per acre. Even in denser places, such as Los Angeles, there is plenty of room to build.

California's growth has slowed because the state has made it increasingly difficult to build new homes. There is an almost perfect correlation between the growth of an area and the amount of housing that is permitted in that area. California has some of the toughest land-use regulations in the country, which are often justified as environmental measures. When high housing demand is met with restrictions -- not construction -- California homes become unaffordable and new construction goes somewhere else.

Local anti-growth activists don't have the ability to stop new construction in the U.S. as a whole. After all, households continue to form, and they need to go somewhere. When California won't build, people go to less-restrictive places, such as Atlanta, Houston or Phoenix, which happily erect new housing. The pro-development policies in these places promote affordability, but they do so at an environmental cost. Carbon emissions are much higher in these growing areas than they are in California.

The environmental opponents of California growth may sometimes accept that by pushing development from Los Angeles to Texas, their anti-growth policies increase carbon emissions. They then emphasize that California's water crisis makes further expansion impossible. But today, the overwhelming majority of water in California is directed to farms, not people. Using 10% of the state's agricultural water for new households could address the water needs of a massive increase in state population. California's water shortage is real, but it calls for more efficiency, conservation and new technologies, not wholesale growth restrictions that increase carbon emissions.

The state took an important step by instituting environmental impact reviews for new development 35 years ago. But such reviews only make sense if they are complete. A full review also would ask about the effects on the environment if a development is pushed somewhere else, like the desert outside Las Vegas. More complete environmental reviews, showing the costs of both building and not building, would reveal the full environmental benefits of building in L.A.

Stopping new development may seem green, but it isn't. When new homes aren't built in California, they are built in other places that are far less environmentally friendly. The best way for Californians to save the planet is to tear down the barriers that stop new development and encourage more people to live in a state where nature, not artificial energy, makes living pleasant year-round.